1. Field of the Invention
The present invention relates to a cooling unit having a tube and a plurality of heat-radiating fins, in which the heat of the liquid coolant flowing in the tube is radiated from the fins. The invention also relates to an electronic apparatus such as a portable computer with such a cooling unit.
2. Description of the Related Art
A CPU is incorporated in, for example, notebook-type portable computers. The heat that the CPU generates while operating increases as its data-processing speed rises or as it performs more and more functions. The higher the temperature of the CPU, the less efficiently it operates. To cool the CPU, so-called “cooling system of liquid cooling type” have been put to use in recent years. The cooling system uses a liquid coolant that has a far higher thermal conductivity than air.
U.S. Pat. No. 6,510,052 B2 discloses a cooling system of liquid cooling type, designed for use in notebook-type portable computers that have a main unit and a display unit. This cooling system has a heat receiving head, a heat radiator, a circulation path for circulating liquid coolant, and an intermediate cooling unit. Once the cooling system has been incorporated into a portable computer, the heat-receiving head is provided in the main unit of the computer and thermally connected to the CPU thereof. The heat radiator is provided in the display unit of the computer and located adjacent to the display device that is provided in the display unit. The circulation path connects the heat receiving head and the heat radiator.
The intermediate cooling unit is arranged on the circulation path. The intermediate cooling unit has a main body and an electric fan. The main body has a first passage, a second passage, and a plurality of heat-radiating fins. Liquid coolant flows in the first passage after it is heated in the heat-receiving head. Cooling air supplied by the electric fan flows in the second passage. The heat-radiating fins protrude from the bottom of the second passage. The fins extend straight in the direction of the cooling airflows. The cooling air passes through the gap between any adjacent fins.
In this cooling system, the liquid coolant absorbs the heat of the CPU in the heat receiving head. The liquid coolant thus heated is supplied through the circulation path to the intermediate cooling unit. In the intermediate cooling unit, the coolant flows through the first passage. While the coolant is flowing through the first passage, part of heat propagates from the coolant to the main body. The cooling air flowing in the second passage cools the main body and takes the heat of the CPU transmitted to the main body. As a result, the liquid coolant heated in the heat receiving head is cooled by virtue of heat exchange with the cooling air, before it reaches the heat radiator.
The liquid coolant cooled in the intermediate cooling unit is supplied to the heat radiator. As the coolant passes through the heat radiator, it releases the heat of the CPU. The liquid coolant cooled in the heat radiator is supplied back to the heat receiving head via the circulation path. In the heat receiving head, the coolant absorbs heat from the CPU. As the coolant is so circulated, the heat is transferred from the CPU first to the intermediate cooling unit and then to the heat radiator.
In the conventional cooling system, the electric fan of the intermediate cooling unit can supply cooling air, but in only one direction with respect to the axis of rotation of its impeller. This restricts the shape that the second passage may have and the number of fins that can contact the cooling air. Consequently, the total area at which the fins contact the cooling air is insufficient. To make matters worse, each heat-radiating fin is connected to the bottom of the second passage, at its narrow end. Inevitably, heat propagates to each fin in a smaller amount than otherwise, from the liquid coolant flowing in the first passage.
Consequently, the surface temperature of each heat-radiating fin cannot rise as much as is desired. That is, the heat of the liquid coolant cannot be radiated with high efficiency.